The present invention relates to wireless communications, and more particularly, to wireless communication methods and systems using multiple sectored cells.
The communications industry has long sought increased capacity communication systems that could bring robust communications to the world""s population. Much of today""s communication traffic is in the form of information carriers that are encoded with digital data representing information to be transported across a communication link. The information transported across the link may often include, for example, voice or video information, as well as textual information or raw data for a particular application.
With the increased use of the Internet and other forms of data communication in recent years, there has been an exponential increase in worldwide data traffic. The increased demand for data communications has essentially outpaced the capacity of existing systems, creating a need for higher capacity communication systems. The capacity of a communication link generally refers to the amount of data that can be reliably transported over the link per unit time and is typically measured in terms of data bits per second (bps).
Wireless communication systems are recognized as an effective method of interconnecting users. Wireless communication systems may be preferable, particularly in geographic locations such as congested urban areas, remote rural areas, or areas having difficult terrains, where it may be difficult and/or cost-prohibitive to deploy wire conductors or fiber optics. Rather than transporting information on carriers over a physically xe2x80x9ctangiblexe2x80x9d communication link such as a wire conductor or fiber optic cable, wireless systems radiate information carriers in xe2x80x9copen spacexe2x80x9d throughout a coverage area. The communication link in wireless systems generally may be defined by the spatial profile of the radiated information carriers.
Generally, the information carriers radiated in wireless communication systems have particular carrier frequencies and predetermined bandwidths within a designated frequency spectrum for a given communication link. In particular, a given information carrier may represent a single channel over which to transport information, or may represent a xe2x80x9cchannel setxe2x80x9d including several channels over which to transport information. For example, a frequency band (i.e., a portion of the designated frequency spectrum) centered around a particular carrier frequency may be divided into a number of smaller bandwidth frequency channels, wherein each channel may carry unique information. Such a scheme commonly is known as Frequency Division Multiple Access (FDMA). Alternatively, an information carrier having a particular carrier frequency may be divided into a number of time slots, wherein each time slot represents a channel that may carry unique information. Such a scheme commonly is known as Time Division Multiple Access (TDMA). Yet other examples of techniques to partition a frequency band into a set of channels include various coding schemes to uniquely identify channels within a set, such as Code Division Multiple Access (CDMA) which uses a unique pseudo-noise digital code (PN code) to encode and decode each channel of a channel set, and various Orthogonal Frequency Division Multiplexing (OFDM) techniques (including VOFDM, COFDM, SC-OFDM, etc.).
Historically, wireless communication systems have found great applicability for communicating with mobile users. Generally, conventional mobile wireless communication systems are designed by dividing a coverage area into a number of cells in a honeycomb-like manner. For purposes of illustration, the cells in the coverage area often are represented as either essentially circular or hexagonal in shape. For purposes of this disclosure, it should be appreciated that one or both of a circular or hexagonal cell shape may be used interchangeably in the drawings to represent a typical cell in a wireless communication system coverage area.
FIGS. 1A and 1B show two examples of common arrangements of cells in a conventional mobile wireless communication system. Generally, it is assumed that each cell in such an arrangement has essentially a same radius and covers an approximately circular area, as shown in FIGS. 1A and 1B. From FIGS. 1A and 1B, it should be readily apparent that each cell in an inner portion of the coverage area is surrounded by 6 other cells.
For wireless communication systems in general, frequency spectrum is a valuable commodity. Typical goals of a wireless communication system designer include reaching as many users as possible via broadband high capacity communication links, and doing so by using as little frequency spectrum as possible. In view of the foregoing, a variety of frequency spectrum reuse plans and cell layouts have been developed, primarily for use in mobile wireless communication systems, to reuse portions of frequency spectrum in a number of cells in a coverage area while attempting to minimize interference amongst cells in which the same frequency spectrum is used. By dividing a coverage area into a number of cells, and reusing portions of frequency spectrum in some of the cells, the information carrying capacity of the reused portions of frequency spectrum is essentially multiplied by the number of cells in which the portions are used.
FIGS. 1A and 1B show two common frequency spectrum reuse plans for conventional mobile wireless communication systems. In each of the cells shown in FIGS. 1A and 1B, radiation (i.e., representing one or more information carriers) is transmitted from approximately the center of the cell in an omnidirectional manner throughout the cell. The radiation transmitted in each cell is allocated a particular frequency band within the allotted frequency spectrum for the system. The cells are arranged relative to one another such that neighboring cells do not use the same frequency band.
FIG. 1A shows a coverage area that employs a frequency spectrum reuse plan using three different frequency bands, A, B, and C. The use of three different frequency bands in the cell arrangement of FIG. 1A insures that no two adjacent cells use the same frequency band. The three different frequency bands each may be reused a number of times to build up the honeycomb pattern of the coverage area shown in FIG. 1A. It is noteworthy in FIG. 1A that, starting from a center cell 20 which uses the frequency band A, the nearest cells 211-216 which also use the frequency band A are removed from the center cell 20 by one xe2x80x9clayerxe2x80x9d of intervening cells that surround the center cell 20.
Another possible frequency spectrum reuse plan for the cells of FIG. 1A is to employ different radiation polarizations amongst cells using a same frequency band. For example, the A cells may use a first frequency band having a first polarization, the B cells may re-use the first frequency band with an orthogonal polarization to the first polarization, and the C cells may use a second frequency band. Alternatively, cells using a same frequency band may use different time slots or channel codes, as discussed above, to differentiate the information channels amongst the cells. In view of the foregoing, the designations A, B, and C in FIG. 1A each may refer to one of three different cell xe2x80x9cconfigurations,xe2x80x9d wherein each cell configuration may be uniquely identified from another cell configuration by at least one of frequency band, polarization, time slot, or channel code, for example. Accordingly, as seen in FIG. 1A, in a coverage area having a honeycomb pattern cell arrangement employing three different cell configurations, a xe2x80x9cbuffer layerxe2x80x9d of one cell is insured between two cells having the same configuration (e.g., using the same frequency band).
FIG. 1B shows a similar honeycomb pattern arrangement of cells in a coverage area employing seven different cell configurations (e.g., seven different frequency bands). In particular, a center cell 22 of FIG. 1B is designated as having a configuration F, while each of six cells surrounding the center cell 22 have a different configuration, namely, A, B, C, D, E, and G. By employing seven different cell configurations in the cell arrangement of FIG. 1B, a buffer layer of two intervening cells having different configurations is insured between two cells having the same configuration, as illustrated by the cells 241-246 which use the same configuration F as the center cell 22.
Other proposed solutions for increasing the capacity of wireless communication systems have been directed to point-to-multipoint configurations for primarily stationary users in a coverage area. In these configurations, often a coverage area is divided up in a pie-like fashion into a number of wedge-shaped sectors, as shown in FIG. 1C, rather than a honeycomb pattern of cells, as shown in FIGS. 1A and 1B. Such systems typically employ a sectored antenna system, which permits the reuse of frequency spectrum amongst multiple sectors within the coverage area. In the example of FIG. 1C, adjacent sectors of the coverage area use different frequency bands, and alternate sectors use a same pair of carrier frequencies (e.g., F1-F3 for pair A and F2-F4 for pair B) for full duplex (i.e., two way) information channels. By dividing a coverage area into a number of sectors rather than a number of cells, and reusing one or more frequency bands in some of the sectors, the information carrying capacity of the reused frequency bands is essentially multiplied by the number of sectors in which the bands are used.
In sum, frequency spectrum reuse may increase the information carrying capacity of a given xe2x80x9cslicexe2x80x9d of frequency spectrum in a wireless communication system. However, frequency spectrum reuse typically requires a sufficient degree of isolation amongst cells of a cellular coverage area (as discussed above in connection with FIGS. 1A and 1B), or sectors of a sectored coverage area (as discussed above in connection with FIG. 1C) to insure a relatively error-free exchange of information. For sectored coverage areas in particular, frequency reuse, and therefore increased capacity, may be achieved at the expense of increased isolation amongst the sectors.
One embodiment of the invention is directed to a wireless communication system, comprising at least three sectored cells. Each cell is divided into at least three sectors and is assigned at least three different channels such that adjacent sectors of the sectors in each cell use different channels. The cells are arranged using at least three different cell configurations, wherein each cell configuration is uniquely identified by at least one of a particular azimuth orientation of the cell about a center of the cell and particular channel types of each different channel of the at least three different channels used in the cell.
Another embodiment of the invention is directed to a wireless communication system, comprising at least two base stations disposed in a coverage area that includes at least two adjacent cells. Each cell includes a respective plurality of subscriber stations and includes at least one base station disposed approximately at a center of the cell to exchange information over air with the respective plurality of subscriber stations. Each cell has approximately a same radius and spans a 360 degree azimuth angle around the base station. The two adjacent cells define at least one bore axis that passes through the center of each cell. The wireless communication system is constructed and arranged such that each cell is divided into at least three sectors. The base station in each cell exchanges information with the respective plurality of subscriber stations using at least three different channels, wherein adjacent sectors of the at least three sectors in each cell use different channels. The two adjacent cells are arranged with respect to each other such that sectors of the two adjacent cells that are similarly oriented approximately along the bore axis and in which radiation is transmitted by the two base stations in essentially a same direction approximately along the bore axis use different channels.
Another embodiment of the invention is directed to a wireless communication system, comprising at least seven base stations disposed in a coverage area that includes at least seven cells. Each cell includes a respective plurality of subscriber stations and includes at least one base station disposed approximately at a center of the cell to exchange information over air with the respective plurality of subscriber stations. Each cell has approximately a same radius and spans a 360 degree azimuth angle around the base station. A first cell of the seven cells is adjacent with each of six other cells such that the six other cells surround the first cell. The seven cells define a plurality of bore axes, each bore axis passing through the center of each of two cells of the seven cells. The wireless communication system is constructed and arranged such that each cell is divided into 6N sectors, N being an integer. The base station in each cell exchanges information with the respective plurality of subscriber stations using at least three different full duplex channels, wherein adjacent sectors of the 6N sectors in each cell use different full duplex channels. The seven cells are arranged with respect to each other such that sectors of adjacent cells that are similarly oriented approximately along one bore axis and in which radiation is transmitted by at least two of the seven base stations in essentially a same direction approximately along the one bore axis use different full duplex channels.
Another embodiment of the invention is directed to a wireless communication system, comprising K different cell configurations, K being an integer not less than three. Each cell configuration of the K different cell configurations includes a cell having 6N sectors, N being an integer. Each cell uses a same set of C different channels to transport information, C being an integer equal to at least K. The K different cell configurations include K different azimuth orientations of the cells with respect to one another.
Another embodiment of the invention is directed to a wireless communication method, comprising acts of dividing a coverage area into at least three cells, dividing each cell of the at least three cells into at least three sectors, and assigning at least three different channels to each cell of the at least three cells such that adjacent sectors of the at least three sectors in each cell use different channels. The method also includes an act of arranging the at least three sectored cells using at least three different cell configurations, each cell configuration of the at least three different cell configurations being uniquely identified by at least one of a particular azimuth orientation of the cell about a center of the cell and particular channel types of each different channel of the at least three different channels used in the cell.
Another embodiment of the invention is directed to a wireless communication method in a wireless communication system including at least two base stations disposed in a coverage area that includes at least two adjacent cells. Each cell includes a respective plurality of subscriber stations and includes at least one base station disposed approximately at a center of the cell to exchange information over air with the respective plurality of subscriber stations. Each cell has approximately a same radius and spans a 360 degree azimuth angle around the base station. The two adjacent cells define at least one bore axis that passes through the center of each cell. The method comprises acts of dividing each cell into at least three sectors, and assigning at least three different channels in each cell to exchange information between the at least one base station and the respective plurality of subscriber stations, wherein adjacent sectors of the at least three sectors in each cell are assigned different channels. The method also comprises an act of arranging the at least two adjacent cells with respect to each other such that sectors of the at least two adjacent cells that are similarly oriented approximately along the at least one bore axis and in which radiation is transmitted by the at least two base stations in essentially a same direction approximately along the at least one bore axis use different channels.
Another embodiment of the invention is directed to a wireless communication method, comprising acts of dividing a coverage area into a plurality of cells, dividing each cell of the plurality of cells into 6N sectors, N being an integer, and assigning a same set of C different channels to transport information in each cell of the plurality of cells, C being an integer. The method also comprises an act of arranging the plurality of cells using K different cell configurations, K being an integer not less than three, C being equal to at least K, the K different cell configurations including K different azimuth orientations of the cells with respect to one another.